This application is a division of application Ser. No. 12/008,041, filed Jan. 8, 2008. It is well-known to employ inorganic materials in composite articles to strengthen and reinforce the articles. In addition to Increased dimensional stability, addition of the inorganic material provides polymer composites with significantly improved physical and mechanical properties. As one example, glass fibres may be placed into a polymer matrix where the high tensile strength of glass causes the composite to become more rigid. The glass fibres incorporated in the polymer matrix may take various forms: continuous or chopped strands, rovings, woven or non-woven fabrics, continuous or chopped strand mats, etc.
Conventionally, glass fibres are formed by attenuating streams of a molten glass material from a bushing or orifice. The glass fibres may be attenuated by pulling by a winder, which collects filaments into a package or by other equipment or method capable of pulling the fibres. A sizing composition, or chemical treatment, is typically applied to the fibres after they are drawn from the bushing. After the fibres are treated with the sizing, which is typically in aqueous form, they may be dried in a package, chopped, or kept in the wet state before downstream processing.
Fibreglass may be mixed with a polymeric resin in an extruder and supplied to a compression- or injection-moulding machine to be formed into glass fibre-reinforced plastic composites. Typically, polymer pellets and fibreglass are fed together or separately into an extruder. During the extrusion process using single or twin-screw machines, the resin is melted and the fibres are dispersed throughout the molten resin to form a fibre/resin mixture. Next, the fibre/resin mixture may be degassed, cooled, and formed into pellets. The dry fibre strand/resin dispersion pellets are then fed to a moulding machine and formed into moulded composite articles that have a substantially homogeneous dispersion of glass fibre strands throughout the composite article.
Alternatively, in the process using continuous filaments, fibreglass filaments are mixed with the molten resin in an extruder with the screw geometry designed to mix the matrix with fibres without causing significant damage to the fibres. Obtained extruded materials are then subjected to compression moulding to form long-fibre reinforced thermoplastic materials with significantly improved mechanical properties due principally to the fibres having a higher aspect ratio.
Various chemical treatments exist for inorganic surfaces such as glass fibres to aid in their processability and applications. After fibre formation and before bundling, the filaments or fibres may be treated with a coating composition (hereinafter referred to as a “sizing composition”) that is applied to at least a portion of the surface of the individual filaments to protect them from abrasion, improve the chemical or physical bonding, and to assist in processing. As used herein, the term “sizing composition”, refers to any such coating composition applied to the filaments after forming. Sizing compositions may provide protection for subsequent processing steps, such as those where the fibres pass by contact points as in the winding of the fibres and strands onto a forming package, drying the sized fibres to remove the water and/or other solvent or melting of the film former on the fibre surface, twisting from one package to a bobbin, beaming to place the yarn onto very large packages ordinarily used as the warp in a fabric, chopping in a wet or dry condition, roving into larger bundles or groups of strands, unwinding, and other downstream processes. In addition, sizing compositions can play a dual role when placed on fibres that reinforce polymeric matrices in the production of fibre-reinforced plastics. In such applications, the sizing composition can provide protection as well as compatibility and/or chemical bonding between the fibre and the matrix polymer. Conventional sizing compositions typically contain one or more film forming polymeric or resinous components, glass-resin coupling agents, and one or more lubricants dissolved or dispersed in a liquid medium. The film forming component of the sizing composition is desirably selected to be compatible with the matrix resin or resins in which the glass fibres are to be embedded.
Many types of polymers may be reinforced by inorganic materials. Of particular note are those polymers formed by ring-opening polymerization reactions. Polyamides (PA), such as poly(caprolactam), commonly know as “Nylon-6” or “polyamide-6”, are examples of resins formed by ring-opening polymerization that are frequently reinforced by glass fibres. There is a need to provide glass-reinforced polyamide composites with high glass loading; however, one of the barriers is the high polymer viscosity of the polyamide in the molten state. This high viscosity hinders the dispersion of the glass fibres throughout the molten resin when the fibre/resin mixture is formed.
Anionic-catalysed ring-opening polymerization of lactams has become a commercially significant method for preparation of PA resins since these polymerizations can be conducted at relatively low temperatures and under atmospheric pressures. Caprolactam is by far the most studied lactam for such reactions and Nylon-6 prepared by this route compares favorably in properties with that prepared by conventional hydrolytic polymerization. Fast reaction kinetics, absence of by-products, and the crystalline nature of the Nylon so produced also makes anionic polymerization of lactams a compelling choice for several industrial applications, including reactive extrusion, reactive thermoplastic pultrusion, reaction transfer molding, D-LFT, compression and injection molding, and reaction injection molding.
In its various embodiments, the present invention combines the processes of forming and loading the inorganic component of a reinforced resin with the ring-opening polymerization of a suitable monomer. The invention thereby overcomes any high viscosity issue associated with combining fibres with resins, provides improved interfacial adhesion between the polymer matrix and the inorganic reinforcing material, and thereby provides improved composite materials.